Generally, a fuel pump has an impeller rotatably disposed in a pump room and a motor that rotatably drives the impeller. Such a fuel pump may be used for suctioning a fuel from a fuel tank and for transferring the fuel to an internal-combustion engine. For example, a brushless motor is used for a fuel pump that is disclosed in a patent document 1 (i.e., Japanese Patent Laid-Open No. JP-A-2013-17303). A rotor core of a rotor of this brushless motor includes an inner core that is engagingly fixed onto a shaft by fitting and a permanent magnet that is disposed on an outside of the inner core. The permanent magnet has a cylinder part and tabular ends located on both ends of the cylinder part. Thus, the amount of the permanent magnet used in the core is reduced as a result of the inner core.
The permanent magnet in the above configuration is provided as a bonded magnet which is formed by injection molding a mixture of material including resin and magnetic particles. The bonded magnet disposed on the inner core is attached on an outer surface of the inner core. Further, a difference between a coefficient of a linear expansion of the resin that is used in the bonded magnet and that of a metal inner core may cause a crack in the permanent magnet over time. The cracking may be the result of repeated expansion and contraction of the rotor core due to the temperature change.